Singulators are used when a clump or pack of items are collected, and it is desired to transport them singly for further processing, such as packing, counting, or grading. A particular problem is met when it is desired to pack items into bags, for instance fruits that are portioned by counting or weighing. If the dimension of the fruit is so large that two pieces of fruit cannot pass the opening of the bag simultaneously, there is a considerable risk of jamming, which causes delays. Jams may be sorted out, but it takes time, has to occur against the friction of the conveyor belt that carries the fruit, and against the time pressure of more fruit arriving. In the case of grading, if the product is not singulated properly and overlaps appear, correct grading is not possible or very difficult as it can be very hard to distinguish between the items. For this reason it is considered preferable to have the fruit arrive one at a time, but in quick succession.
One solution for this may be found in U.S. Pat. No. 5,314,056, which describes a conveying device having a guide trough extending longitudinally from a receiving end to a discharge end, the trough having inclined and transversely-opposed sidewalls in which travels an endless feed belt longitudinally through the guide trough from the receiving end to the discharge end, the feed belt having upwardly extending outer portions which are slideably supported on the inclined sidewalls of the guide trough, the feed belt forming a concave conveyor surface for conveying food articles through the guide trough. The trough with the upwards-facing conveying feed belt is continuously vibrated. The combination of the two movements ensures the conveying and singulation, however it is a complex apparatus with fast-moving parts and involving wear of the feed belt mechanism. Another problem with this principle of operation is that it is not capable of quick start and stop, which is a requirement in high-speed handling of products.